This invention relates to a vibrator and a vibratory gyroscope used for an angular rate sensor measuring a turning angular rate in a turning system, a device for measuring a linear acceleration and a method of measuring a turning angular rate.
Up to now, as an angular rate sensor used for detecting a turning angular rate in a turning system, a vibratory gyroscope using a piezoelectric material has been used for detecting position of an aircraft, a ship and a space satellite. Recently, the gyroscope is used in a car-navigation system, a movement detecting mechanism in a VTR or a still camera.
Such a vibratory gyroscope utilizes a Coriolis force, which is generated when an angular movement is applied to a vibrating object in a direction perpendicular to the vibratory direction. Its mechanism may be understood by using a dynamic model (for example, xe2x80x9cHandbook of Elastic Wave Device Technologiesxe2x80x9d (Danseiha-Sosi Gijutsu Handbook) published by Ohm, Inc., pp. 491 to 497). Various kinds of piezoelectric vibratory gyroscopes have been proposed. For example, a Sperry tuning-fork gyroscope, a Watson tuning-fork gyroscope, a regular-triangle prism-shaped tuning-piece gyroscope, a cylindrical tuning-piece gyroscope are known.
The inventors have studied various applications of vibratory gyroscopes, and have tried to use a vibratory gyroscope as a turning rate sensor in a car control system of an automobile body turning rate feedback system. Such a system detects the direction of a steering wheel itself by a turning angle of the wheel. At the same time, the system detects a turning rate of the actually turning car body by means of the vibratory gyroscope. Then the system determines a difference between the direction of the steering wheel and the actual body turning rate by comparing them with each other, and attains a stable body control by compensating a wheel torque and a steering angle on the basis of this difference.
However, any example of the above-mentioned former piezoelectric vibratory gyroscopes can detect a turning angular rate only when arranging its vibrator in parallel with the axis of turning (what is so called xe2x80x9cvertical arrangementxe2x80x9d). The turning axis of a turning system to be measured is usually perpendicular to the gyroscope mounting part. Accordingly, when mounting such a piezoelectric vibratory gyroscope, it has been impossible to shorten the piezoelectric vibratory gyroscope in height, namely, to reduce the piezoelectric vibratory gyroscope in size in the direction of the turning axis.
Recently, a piezoelectric vibratory gyroscope, capable of detecting a turning angular rate even when arranging a vibrator perpendicularly to the turning axis (so called xe2x80x9chorizontal arrangementxe2x80x9d), was proposed in a Japanese laid-open publication Tokkaihei No. 8-128833. However, even such a vibratory gyroscope has a limit to reduce the vibratory gyroscope in size in the direction of the turning axis.
An object of the invention is to provide a novel vibratory gyroscope comprising a vibrator extending in a given plane, and when the vibrator is subjected to a turning in the plane, the gyroscope being capable of detecting an angular velocity of the turning.
The invention provides a vibrator to be turned around a predetermined turning axis, the vibrator comprising at least plurality of vibration systems which are formed within a specified plane intersecting the turning axis, the plurality of vibration systems comprising a first vibration system whose vibration includes a radial vibration component, in which the center of gravity of the first vibration system vibrates in a radial direction in the specified plane with respect to the center of gravity of the vibrator, and a second vibration system whose vibration includes a circumferential vibration component, in which the center of gravity of vibration of the second vibration system vibrates in the specified plane circumferantially, that is, along a circle with the center of gravity of the vibrator as its center.
The invention also provides a vibrator comprising a base portion and a plurality of vibration systems, each vibration system extends radially from the edge of the base portion, the base portion and the vibration systems extend in a specified plane.
The invention also provides a vibratory gyroscope for detecting a turning angular rate in a turning system, comprising said vibrator, an exciting means provided in one of a first vibration system and a second vibration system for exciting a driving vibration in the vibrator, and a detecting means provided in the other of the first vibration system and the second vibration system for detecting a detecting vibration in the vibrator when the vibrator is turned.
The invention also provides a vibratory gyroscope comprising a vibrator, an exciting means for exciting a driving vibration in the vibrator and a detecting means for detecting a detecting vibration in the vibrator when the vibrator is turned, wherein the vibrator comprises a plurality of vibration systems extending in a specified plane intersecting a turning axis, the exciting means being provided in at least one of the vibration systems, and the detecting means being provided in at least one of the vibration systems in which the exciting means is not provided.
The invention also provides a vibratory gyroscope comprising a vibrator, an exciting means for exciting a driving vibration in the vibrator and a detecting means for detecting a detecting vibration in the vibrator when the vibrator is turned, the vibrator extending in a specified plane and comprising a plurality of vibration systems, the exciting means and the detecting means being provided in the different vibration systems, the center of gravity of the whole driving vibration in the vibrator being positioned within a domain near the center of gravity of the vibrator.
The invention also provides a vibratory gyroscope for detecting a turning angular rate in a turning system, the vibratory gyroscope comprising a vibrator to be subjected to a turning around a specified turning axis, exciting means for exciting a driving vibration in the vibrator and detecting means for detecting a detecting vibration in the vibrator when turning the vibrator, the vibrator extending in a specified plane and comprising a plurality of vibration systems, the exciting means and the detecting means being provided in the different vibration systems, the center of gravity of the vibrator being located within a domain in which displacements caused by the driving vibration are small when exciting the driving vibration in the vibrator.
The invention also provides a vibratory gyroscope for detecting a turning angular rate in a turning system, the vibratory gyroscope comprising a vibrator to be subjected to a turning around a specified turning axis, exciting means for exciting a driving vibration in the vibrator and detecting means for detecting a detecting vibration in the vibrator according to the turning of the vibrator, the vibrator extending in a specified plane and comprising a plurality of vibration systems, the exciting means and the detecting means being provided in the different vibration systems, and the center of gravity of the vibrator being located within a domain in which displacements caused by the detecting vibration are small when the detecting vibration is induced in the vibrator.
The invention also provides a method of detecting a turning angular rate around a turning axis in a turning system comprising a vibrator, the vibrator comprising a plurality of driving vibration systems and at least one detecting vibration system extending in a specified plane intersecting the turning axis, the method comprising:
turning the vibrator around the turning axis and exciting driving vibrations in the driving vibration systems at the same time to cancel at least parts of the excited driving vibrations with each other; and
detecting a detecting vibration induced in the detecting vibration system.
The invention also provides a method of detecting a turning angular rate around a turning axis in a turning system comprising a vibrator, the vibrator comprising a plurality of vibration systems extending in a specified plane intersecting the turning axis, the method comprising:
exciting at least radial vibration component in at least one of the vibration systems, the radial vibration component being a vibration in a radial direction in the specified plane with respect to the center of gravity of the vibrator;
exciting a Coriolis force in the circumferential direction based on the radial vibration component when turning the vibrator; and;
detecting a detecting vibration, in the vibrator according to the Coriolis force, within the other vibration system.
The invention also provides a method of detecting a turning angular rate around a turning axis in a turning system comprising a vibrator, the vibrator comprising a plurality of vibration systems extending in a specified plane intersecting the turning axis, the method comprising;
exciting at least a circumferential vibration component in at least one of the vibration systems, the circumferential vibration component being a vibration in the specified plane along a circle with the center of gravity of the vibrator as its center;
exciting a Coriolis force in the radial direction based on the circumferential vibration component when turning the vibrator; and
detecting a detecting vibration, in the vibrator according to the Coriolis force, within the other vibration system.